The invention relates to driving systems in a device for drawing or braking metal bands or sheets, preferably in band lines between endlessly revolving chain systems.
EP-A-0088347 and EP-A-0195096 disclose a braking stand for metal or sheet bands with which the tensile or braking force required during the braking of metal bands can be applied to the surface of the split or non-split band without damaging effects.
The use of the eddy-current effect for braking electrically conductive metal band is described in DE-B 1 288 865. This embodiment is used in practice. The fundamental disadvantage consists in the fact that the desired function does not appear in a useful manner until a band speed of about 50 m/min is reached. The band tension could only be controlled by a change in spacing. The result was unsatisfactory, since, at too close a spacing, contact with the magnet caused relative movements.
A further eddy-current brake is described in laid-open specification DE 195 24 289 A1. The essential difference consists in the fact that the permanent magnets are moved on a circular path. Only one magnetic path is available for the retention effect. In addition, the parallelism of the permanent magnets appears for only a fraction of the period, as a result of which the retention effect is built up in an uneven and substantially reduced manner. In order to be able to apply sufficient specific band tension, the rotational speeds of the braking rollers would have to be brought to orders of magnitude which are no longer controllable. In addition, high drive outputs at a very unfavorable efficiency occur.
The problem underlying the invention is to extend the possible uses of the known braking stand on the one hand and to achieve a specific behavior which is different for the various tasks on the other hand, in particular for the entry, exit and driving conditions of the carriage-like roller blocks in the band-driving region.
This problem is solved by shaping, which produces robust support in the central region. The entry and exit must be of elastic configuration. The design is such that high elasticity in the horizontal direction (band tension direction) is achieved. Furthermore, negligible squeezing is achieved with the invention, as a result of which the flexing work at the entry and exit can be decisively reduced. The lining width corresponds to the chain pitch. The arrangement is made between the running rollers. It is possible with this design to provide a closed contact surface in the driving region. This design requires the synchronous running of the top carriage chain relative to the bottom carriage chain.
A low lining hardness with a relatively thick lining is preferably selected. The metal band is embedded, so that the form errors of the metal band in cross section and the band waviness are compensated for without problem. The clearance spaces created enable the squeezed volume of the elastic lining to flow in a specific manner.
The lining is given a filling piece, e.g. flat-bar steel. This enables the squeezing to be adapted in a specific manner to the functional task by means of stress concentration factor, while the desired inclination of the lining in the tension direction can be effected virtually without restriction.
An appropriate applications [sic] consists in the fact that only one revolving carriage chain is designed as a revolving table. In this case, forces are induced in the band by means of permanent magnets or via electromagnets in order to be able to apply braking or tensile forces. Magnetizable metal band is pulled by the forces of attraction onto the protective strap of the carriage chain and driving forces are produced in accordance with the xcexc-value.
As a further possibility it is suitable for two revolving rollers to be equipped with permanent magnets or with electromagnets and for a parallel, linear, magnetic traveling field to be built up by the applied magnet poles, this magnetic traveling field acting as a linear, revolving eddy-current brake in the electrically conductive band material.
The metal band is heated if the energy is supplied conductively or inductively via the revolving system. This effect may likewise be used in galvanic or other processes.
If the revolving system is equipped with electronic measuring heads, the band thickness, the surface condition, the metallic structures and the like, for example, can be tested very accurately since the metal band and the test head can work in a fixed position for a certain time at identical speed.
An optimum mode of operation is achieved if the mechanical linear drive is operated by an electric linear drive. This embodiment loads the carriage-chain system only in the linear driving region and is therefore appropriate in particular for large forces and high speeds.
If the braking stand is placed in position on a control frame at pass line height, extremely precise control of the band with regard to the band center or band edge becomes possible, since the tilting moment is xe2x80x9cdesigned outxe2x80x9d by this measure. As a result, fluctuations in tension due to vibrations are avoided. This is an important aspect for rolling, stretching, bending and straightening processes.
The braking stand or the control frame may be extended by a band-tension measuring frame. In this case, these units hang in leaf springs. The reaction forces of the band tension are recorded without distortion via measuring cells. This measuring system is able to measure exclusively the horizontal forces with a high repetitive accuracy and, depending on the measuring range, can be set to a few newton.
For high demands, for example in the case of bands of very high surface sensitivity, such as copper or aluminum band, special effects become possible due to the invention, to be precise due to the specific feeding of the chains having the roller blocks into a relatively short clamping and driving region by means of straight guide strips, which at the same time enable the clamping forces to be absorbed. In this way, relatively large pressure forces can be absorbed, these pressure forces being necessary in order to ensure large tensile or retention forces without relative movement between the band and the revolving, carriage-like roller blocks. The specific feeding of the roller blocks is achieved by entry and exit curves at the straight guide strips of the driving region. A highly elastic transition is made possible by specific shaping. The squeezing of the elastic lining is specifically reduced by the insertion of shaped plates.
The design of the electric linear drive has the advantage that the hinge ends of the chain-carriage link plates are only loaded by the deflection and centrifugal forces, whereas the loads from the band tension to be applied only act in the driving region. The dimensioning of the hinges may therefore be restricted to the deflection and centrifugal forces. The wear is thereby minimized.
The driving section may be configured in such a way that current is fed to the metal band conductively or inductively. This solution is preferably used in galvanic processes, when heating the band, for measuring processes on the band and for the build up of magnetic fields, which are used for inducing retention forces. For the current feed, electrically conductive materials are put into the carriage-like roller blocks. The current can be switched on specifically when the roller blocks pass through the driving region. Apart from a better efficiency compared with conventional gas- or oil-fired annealing furnace installations, a great advantage of this measure consists in the fact that the energy supply can be switched off at any time. When the eddy-current method is used, the band tension can be controlled by the opposed speed of the chain carriages, and the retention force can be controlled by varying the frequency.
If the lining carriers of the carriage-chain system are equipped with measuring probes, ideal analyzing conditions are provided by the revolving table. The task of the revolving carriage-chain system is to carry the band and to ensure a fixed band distance from the measuring heads or magnet coils. The dwell time for the test operation can be set by establishing the contact section, since the metal band and the carriage-chain system have the same speed in this region. The application is suitable for band-thickness measurements, stress measurements in the band, surface scanning and other test systems. The current may alternatively be fed from the inside or laterally from outside. The current is switched on and off after the chain carriage has reached the parallel section or before it leaves the parallel section.
Individual magnets or magnet coils, which pass over the entire segmented region, can be supplied with voltage according to the same system. The band is pulled onto the chain carriage via the magnetic forces of attraction. Band tension can be applied via the chain-carriage system as a function of these forces and the xcexc-value. This is also possible by means of permanent magnets. This design is suitable for magnetizable metal bands.